Secret missions North Korea has successfully launched a rocket into orbit, the same day the US Air Force's secretive X-37B spacecraft returned to space.

The rocket, which North Korea says was designed to put a weather satellite into orbit, has been labelled by the United States, South Korea and Japan as a test of technology that could one day deliver a nuclear warhead capable of hitting targets as far as the continental the United States.

"The satellite has entered the planned orbit," North Korea's state news agency KCNA said.

The rocket was launched just before 12:00 pm AEDT, according to defence officials in South Korea and Japan, and easily surpassed a failed April launch that flew for less than two minutes.

There was no independent confirmation it had put a satellite into orbit.

There was no immediate official reaction from Washington, South Korea's major military backer, or from China.

China had expressed "deep concern" over the launch which was announced a day after a visit by a top politburo member to Pyongyang when he met Kim Jong-un.

On Wednesday, China's state news agency Xinhua said North Korea had the "right to conduct peaceful exploration of outer space."

But it added: "Pyongyang should also abide by relevant U.N. Security Council resolutions, including Resolution 1874, which demands (North Korea) not to conduct 'any launch using ballistic missile technology' and urges it to 'suspend all activities related to its ballistic missile programme.'"

The April launch was timed for the centennial of the birth of Kim Il Sung, the founder of North Korea and the grandfather of its current ruler.

Secret shuttle

Seven hours earlier, an Atlas V rocket with a X-37B shuttle on board launched from Cape Canaveral in Florida on a mission about which the US Air Force has offered minimal details.

The US military has described the X-37B program as a way to demonstrate "technologies for a reliable, reusable, unmanned space test platform" following the retirement of NASA's shuttle Orbiter program.

The secretive nature of the equipment on the X-37B has led to speculation in the media over the missions' aims, with some experts believing that the US Air Force is looking at new way of spying.

Space experts believe that the small vehicle, with its ability to return to Earth and head back up, could be part of a state-of-the-art espionage program or may potentially be used to interfere with rival nations' satellites.

It is the second mission of the original X-37B which went into space in 2010 in the program's inaugural flight and stayed in orbit for more than half a year.

A second X-37B vehicle returned to Earth in June after orbiting for 469 days in an endurance test that went far beyond the aircraft's intended flight span of 270 days.

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